BUJUMBURA, Burundi (AFP) - Attackers hurled twin grenades into a crowd in Burundi's capital late on Friday, killing three people, the latest in almost month of deadly violence triggered by the President's bid for a third term.

Thousands of anti-government protesters earlier battled police in the capital Bujumbura, defying one of the heaviest pushes by security forces to end weeks of demonstrations against President Pierre Nkurunziza.

But the grenade blasts - the first such attacks to apparently deliberately target a civilian crowd - mark a deadly twist in the unrest that has sent 110,000 Burundians fleeing as refugees into neighbouring nations.

Deputy police chief, General Godefroid Bizimana, said the unknown attackers aimed to kill, with three dead but also about a dozen maimed or wounded.

"Those who did this had the intention to kill, because the grenades were thrown among women selling fruits, in a big crowd," Bizimana said, adding the attackers escaped.

Meanwhile, protesters torched election materials in two separate attacks south of the capital, electoral commission spokesman Prosper Ntahorwmiye said, destroying voting booths and ballot boxes. "Everything was burned," Ntahorwmiye said.

TWO-DAY TRUCE AND TALKS

More than 20 people have died since the crisis erupted in late April after the ruling party nominated Nkurunziza to stand again in the June 26 presidential election. The crisis deepened last week when a top general staged a failed coup attempt.

Parliamentary polls, initially set for May 26, have been postponed to June 5.

Nkurunziza said in an address to the nation late Wednesday that most of the central African country was secure and that upcoming parliamentary and presidential votes would be peaceful.

But on Friday morning, protesters shouted and blew whistles to try to encourage others to come out onto the streets. By late afternoon, thousands had answered the call. Some looted a beer truck as they celebrated, despite gunfire from police.

"And the government says there is no demonstration in Bujumbura!" said Adolphe, 46, a civil engineer and local resident.

But protesters also announced a two-day weekend truce "to allow the people to bury with dignity those who died for democracy," civil society leader Pacifique Nininahazwe said, but adding a warning that "protests will resume on Monday with even more force."

Nininahazwe said that talks between the protesters, opposition parties and government had been taking place this week.

"We ask the government to show good faith by refraining to shoot protesters," Nininahazwe added. "On our part, we promise a completely peaceful demonstration. If they continue to shoot, we will end the dialogue process."

CHOLERA DEATHS RISING

Opposition and rights groups say that Nkurunziza's bid for a third five-year term violates the constitution and the terms of a peace deal that ended a 13-year civil war in 2006.

Nkurunziza, a former rebel leader and born-again Christian who believes he has divine backing to lead the country, argues that his first term did not count as he was elected by parliament, not directly by the people.

Refugees continue to flee the violence, the majority to neighbouring Tanzania, where over 50,000 refugees are struggling in dire conditions on the shores of Lake Tanganyika.

Cholera has broken out in squalid refugee camps there, with at least 31 people having died and over 3,000 cases in total, with numbers growing by up to 400 cases a day, according to the UN refugee agency.